Ti-containing Phases Research Articles

On the microstructure, corrosion behavior and surface films of the multi-principal element alloy CrNiTiV

A multi-principal element alloy consisting of equi-atomic concentrations of Cr, Ni, Ti, and V, was produced by arc melting. The CrNiTiV alloy was characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and scanning transmission electron spectroscopy (STEM), revealing a complex microstructure containing five phases. The corrosion performance of the alloy was evaluated with cyclic potentiodynamic polarization tests, indicating a low corrosion current density, a high breakdown potential and high repassivation potential. X-ray photoelectron spectroscopy and STEM were carried out after constant immersion in 0.6 M NaCl solution, revealing the passive (surface) film for each of the five phases. The Cr and V dominant phase consisted of an oxidized Cr/V-rich surface film, while the remaining four Ti-containing phases were predominantly TiO2-rich surface films. Ni enrichment and Ti deficiency were observed at the metal/oxide interface in certain Ti-containing phases.

Effect of Cr2O3 on the break temperature and crystallization behavior of Cr-containing molten titanium slag

In the current study, the effect of Cr2O3 on the break temperature and crystallization behavior of Cr-containing molten titanium slag was investigated. The type, composition, and morphology of crystallized phase were analyzed by FactSage, X-ray diffraction (XRD), and scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS). It was found that the break temperature (TBr) of Cr-containing molten titanium slag tended to increase with the increase of Cr2O3 content. When the Cr2O3 content was 4 wt%, the TBr was 1470 °C. With the increase of Cr2O3 content, the Ti-containing phase began to appear at the temperature above the TBr. Moreover, the main crystallized phase that existed at the temperature below the TBr transformed from only anosovite to both anosovite and spinel, indicating that Cr2O3 promoted the precipitation of spinel. The rapid increase in viscosity was mainly determined by the precipitation of anosovite in the slag without Cr2O3. When the Cr2O3 content was 2 wt%, the increased precipitation amount of Ti-containing phase caused the abrupt change in viscosity. As the Cr2O3 content further increased to 4 wt%, the precipitation amounts of anosovite and spinel significant increased, which resulted in the sudden increase in viscosity. This study could provide theoretical support for the comprehensive utilization of Cr-containing molten titanium slag and sustainable development of titanium and chromium resources.

MELT INCLUSIONS IN OLIVINE AS A SOURCE OF INFORMATION ON THE COMPOSITION AND EVOLUTION OF DEEP MELTS OF AILLIKITES (ULTRAMAFIC LAMPROPHYRES) OF THE ILBOKICHI UPLIFT, THE SW SIBERIAN PLATFORM

Aillikites are kimberlite-like rocks, important for understanding the composition and processes occurring in the mantle. Melt inclusions represent a reliable source of information. The paper provides the first results of studies (Raman, EDS) on primary and secondary melt inclusions in olivine from the Ilbokich uplift aillikites. The composition of primary inclusions is close to that of parent melt of aillikites. It was significantly enriched in CO2, H2O, phosphorus and titanium. Phlogopite, diopside, dolomite, calcite, apatite, Ti-containing phases (brookite, perovskite, Ti-magnetite) and lizardite were identified in these inclusions. The similarity of the composition and ratios of the daughter phases with the aillikite matrix indicates a slight change in the parent melt when it is rising to the surface. As to the secondary inclusions, there are wide variations in compositions and a smaller amount of silicates, as compared to the primary ones. The main daughter phases are carbonates, e.g. dolomite, calcite, magnesite and alkaline carbonates. In addition, phlogopite, clinopyroxene, apatite, halite, pyrrhotite and magnetite, graphite and CO2 were discovered. The variability of the compositions of the secondary inclusions might be due to the silicate-carbonate immiscibility that appeared during the rising of the aillikite melt at pressures <4 GPa.

Investigation of Oxidation Behaviors of Al-Mg Alloys with a Grain Refiner at High Temperature

Studies to investigate the oxidation behavior of Al–Mg alloys with Al-5 mass%Ti-1 mass%B master alloy as a grain refiner at high temperature were conducted. The Scheil-Gulliver cooling calculation showed that, in 0.2 mass%Ti-inoculated alloy, TiAl3 was formed before the primary Al formation, which may act as a grain refiner. The optical microstructures showed a significant grain refinement after the addition of 0.2 mass%Ti using Al-5 mass%Ti-1 mass%B master alloy. Moreover, the oxidized cross-sections, throughout the oxidation time, show coarse and dark areas (regarded as oxide clusters), which were nonuniformly distributed in the matrix after oxidation at 500 °C under an ambient atmosphere. In addition, an accumulation of oxygen by diffusion for a long duration led to the growth of blisters after 50 h. At the oxidation temperature, Mg3Ti2Al18 was found to be only stable Ti-containing phase and possibly formed MgO by the interaction with the diffused oxygen.

Better Together: Ilmenite/Hematite Junctions for Photoelectrochemical Water Oxidation.

Hematite (α-Fe2O3) is an earth-abundant indirect n-type semiconductor displaying a band gap of about 2.2 eV, useful for collecting a large fraction of visible photons, with frontier energy levels suitably aligned for carrying out the photoelectrochemical water oxidation reaction under basic conditions. The modification of hematite mesoporous thin-film photoanodes with Ti(IV), as well as their functionalization with an oxygen-evolving catalyst, leads to a 6-fold increase in photocurrent density with respect to the unmodified electrode. In order to provide a detailed understanding of this behavior, we report a study of Ti-containing phases within the mesoporous film structure. Using X-ray absorption fine structure and high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy, we find that Ti(IV) ions are incorporated within ilmenite (FeTiO3) near-surface layers, thus modifying the semiconductor–electrolyte interface. To the best of our knowledge, this is the first time that an FeTiO3/α-Fe2O3 composite is used in a photoelectrochemical setup for water oxidation. In fact, previous studies of Ti(IV)-modified hematite photoanodes reported the formation of pseudobrookite (Fe2TiO5) at the surface. By means of transient absorption spectroscopy, transient photocurrent experiments, and electrochemical impedance spectroscopy, we show that the formation of the Fe2O3/FeTiO3 interface passivates deep traps at the surface and induces a large density of donor levels, resulting in a strong depletion field that separates electron and holes, favoring hole injection in the electrolyte. Our results provide the identification of a phase coexistence with enhanced photoelectrochemical performance, allowing for the rational design of new photoanodes with improved kinetics.

Formation mechanism of Ti(C, N) solid solution in Al-brown fused alumina refractory at 1973 K in flowing N2

Brown fused alumina is a cost-effective alumina material, and the state of Ti in alumina has a great influence on its high-temperature performance. In this paper, the Ti-containing phases in brown fused alumina particles and Al-brown fused alumina refractory were successfully transformed into Ti(C,N) at 1973 K in flowing N2. The evolution of the Ti-containing phases in brown fused alumina under high temperature and nitrogen conditions was investigated by XRD, SEM and EDS. The results show that the Ti-containing phases in brown fused alumina include Ti2O3, Ti(C,N,O), TiFeSi2, Ca0·95Mg0·9Al10·1(Ti)O17 and a low-melting point Ca3Al2Si3(Mg,Ti)O12 phase. Under high temperature and nitrogen conditions, the TiO2[liquid], MgO[liquid] and SiO2[liquid] in the low-melting point phase are transformed into Ti(C,N), Mg(g) and SiO(g), while they are supplemented from Ti2O3, Ti(C,N,O) and Ca0·95Mg0·9Al10·1(Ti)O17. After heat treatment at 1973 K for 3 h, Ti2O3 and Ti(C,N,O) disappear, Ca0·95Mg0·9Al10·1(Ti)O17 is transformed into plate-like Ca0·55Al11O17.05, and Ti(C,N) is formed on the surface of the corundum particles. The formation of Ti(C,N) reduces the porosity of the brown fused alumina particles and increases their strength.

High-Temperature Active Soldering of SiC Particle-Reinforced Al-MMC Using a Novel ZnAlGaMgTi Filler Metal

In order to broaden the application of SiC particle-reinforced aluminum matrix composite in electronics packaging, newly developed ZnAlGaMgTi filler with a low melting point of 418-441 °C was utilized as filler metal for active soldering of aluminum matrix composites (70 vol.%, SiCp/Al-MMCs) for the first time. The effect of loading pressure on joint properties of ZnAlGaMgTi active filler was investigated. The experimental results indicated that novel filler could successfully solder Al-MMCs, and the presence of Mg in the filler enhanced the penetration of Zn, while the forming of Zn-rich barrier layer influenced the active element MPD (melting point depressant) diffusion into parent composite, and the bulk-like (Mg-Si)-rich phase and Ti-containing phase were readily observed at the interface and bond seam. With the increase in loading pressure, the runout phenomenon appeared more significant, and the filler foil thickness and the Zn penetration depth varied pronouncedly. Sound joints with maximum shear strength of 29.6 MPa were produced at 480 °C at 1 MPa, and the crack occurred adjacent to the boundary of SiC particle and then propagated along the interface. A novel model describing the significant mutual diffusion of Al and Zn atoms between the parent material and solder was proposed.

STUDY OF LOW-TITANIUM SLAG AND SODA BAKING PROCESS

The article presents study results of soda and low-titanium slag baking, where the slag is produced during processing of titanium magnetite concentrate. The purpose of baking is to change the mineralogical composition of Ti-containing phases and obtain a product suitable for chemical separation of titanium dioxide from impurities. The X-ray phase analysis revealed that the obtained titanium slag belonged to the spinel-anosovit type. The article studies the factors influencing the baking process: the slag to soda mass ratio, the process duration, the temperature and the size of slag particles. The thermal analysis of the slag and soda baking process revealed that the optimum process temperature was 900°C. This temperature ensured formation of sodium titanates and a cake of sufficient porosity. The article demonstrates that effective decomposition pro cess requires a pretreatment of titanium slag by fine grinding. It was found that grinding of titanium slag particles to 40 μm contributes to more complete decomposition of the anosovite and formation of sodium titanates. It was found that during titanium slag and soda baking at the slag to soda mass ratio of 1 : 1,05, decomposition of anosovite occurred, and virtually all titanium was bound to sodium titanates. Optimal process conditions were determined as follows: slag to soda mass ratio – 1 : 1,05, baking temperature – 900 ° C, duration – 60 minutes and slag particle size – 40 μm. During baking, the titanium-containing slag phases were converted into Na 2 TiO 3 and Na 8 Ti 5 O 14 . The presence of a significant amount of silicon dioxide and the sodium-magnesium silicate phase was observed in the cake. The electron microprobe analysis of the cake showed that impurity elements were adsorbed on the particles of formed Na 2 TiO 3 .

Correlated extended X-ray absorption fine structure and transmission electron microscopy studies the microstructure of low friction Ti–C–N films

The microstructures of Ti–C–N films were investigated by extended X-ray absorption fine structure and transmission electron microscopy. The expected Ti-containing phases, TiN, are not formed in low Ti content film. The local structure around the central Ti atoms as deduced from EXAFS shows the Ti atoms mainly to be situated in disordered regions, possibly small Ti–C or Ti–N clusters without long-range crystalline order. With increasing the Ti content, the film alters the coherent interfaces and forms a nanocomposite structure. Our results indicated increased Ti co-ordination shell disorder in Ti–C–N coatings with decreasing Ti composition. Wear rate and friction coefficient of films decrease as the Ti composition increases.

Crystalline Al1 − x Ti x phases in the hydrogen cycled NaAlH4 + 0.02TiCl3 system

The hydrogen (H) cycled planetary milled (PM) NaAlH4 + 0.02TiCl3 system has been studied by high resolution synchrotron X-ray diffraction and transmission electron microscopy during the first 10 H cycles. After the first H absorption, we observe the formation of four nanoscopic crystalline (c-) Ti-containing phases embedded on the NaAlH4 surface, i.e. Al2Ti, Al3Ti, Al82Ti18 and Al89Ti11, with 100% of the originally added Ti atoms accounted for. Al2Ti and Al3Ti are observed morphologically as a mechanical couple on the NaAlH4 surface, with a moderately strained interface. Electron diffraction shows that the Al82Ti18 phase retains some ordering from the L12 structure type, with the observation of forbidden (100) ordering reflections in the fcc Al82Ti18 lattice. After 2 H cycles the NaAlH4 + 0.02TiCl3 system displays only two crystalline Ti-containing phases, Al3Ti and Al89Ti11. After 10 H cycles, the Al89Ti11 is completely converted to Al85Ti15. Al89Ti11, Al85Ti15 and Al3Ti do not display any ordering reflections, and they are modeled in the A1 structure type. Quantitative phase analysis indicates that the Al3Ti proportion continues to increase with further H cycles. The formation of Ti-poor Al1 − x Ti x (x < 0.25) phases in later H cycles is detrimental to hydrogenation kinetics, compared to the starting Ti-richer near-surface Al2Ti/NaAlH4 interface present during the first absorption of hydrogen.

Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques

Typical red–brown (Fe-rich) and high-quality white–grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to 228Ac ( 232Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to 228Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO 2 polymorphs). SEM-EDS indicated the presence of Ti–Fe–containing phases (e.g. ilmenite, FeTiO 3), chromite (Cr-spinel) and besides LREE-minerals (mostly bastnäsite/parisite-group) and zircon (ZrSiO 4) hosting a part of the bulk Th. The presence of Th in diaspore and in Ti-containing phases (not detected by SEM-EDS as in the case of REE-minerals and zircon) was investigated, into distinct pisoliths of Fe-depleted bauxite, using μ-XRF and μ-XAFS in the SUL-X beamline of the ANKA Synchrotron facility (KIT, Germany). XAFS spectra of Th salts and Th-containing reference materials were obtained as well. Accordingly it was revealed, for the first time in the literature, that Ti-phases, and particularly anatase, host significant amounts of Th. This novel conclusion was complementary supported by LA-ICP-MS analyses indicated an average of 73 ppm Th in anatase grains together with abundant Nb (3356 ppm), Ta (247 ppm) and U (33 ppm). The Th L III-edge XAFS spectra as compared to reference materials, give also evidence that Th 4+ may not replace Ti 4+ in distorted [TiO 6] fundamental octahedral units of anatase and ilmenite lattice (CN = 6). The occupation of either extraframework sites of higher coordination (CN = 6.9 or even CN = 7.4), according to EXAFS signals evaluation, or of defected/vacant (**) sites is more probable. This is likely explained by the difficulty of Th 4+ to replace directly Ti 4+ in [6]-coordinated (octahedral) sites due to the large difference in the relevant ionic radii (0.940 and 0.605 Å respectively).

Identification of the matrix elastoplastic properties in reinforced active brazing alloys

The mechanical response of the reinforced active alloy Incusil (TM) ABA (R)-SiC is studied. Specimens with up to 27 vol.% SiC particles are produced and tested in tension. The presence of the reinforcement leads to modifications in the alloy mechanical response and microstructure, with a decrease in the volume fraction of Ti-containing phases. To study the in situ response of the matrix material in the composites an inverse homogenization approach is proposed. The identified responses of the matrix materials are softer than that of unreinforced Incusil (TM) ABA (R). These results are experimentally confirmed by studying the effect of Ti-addition to Incusil (TM) ABA (R), a braze alloy whose composition is close to that of Incusil (TM) ABA (R) without Ti. (c) 2008 Elsevier Ltd. All rights reserved.

Multi-walled carbon nanotubes decorated with titanium nanoparticles: synthesis andcharacterization

A chemical route to decorate MWCNTs by titanium nanoparticles has been developed.MWCNTs, grown by catalytic decomposition of propane, have been used to prepareintercalated K-MWCNTs, which are then reacted with Ti(IV) isopropoxide. The amount ofTi present in the nanostructure is 8.7 wt%. Several techniques have been used for a detailedcharacterization of MWCNTs decorated by Ti nanoparticles, such as transmission electronmicroscopy (TEM), selected-area electron diffraction (SAED), high resolution transmissionelectron microscopy (HREM) and electron energy loss spectroscopy (EELS) as well asRaman spectroscopy and x-ray diffraction (XRD). Titanium is found to be present asα-Ti(hcp) dispersed in very small particles, the size of the largest being∼2 nm. The Ti-containing phase appears to be fairly homogeneously distributed in the spacebetween the two sides of a MWCNT. No intercalation of Ti between the CNT walls hasbeen detected.

Synchrotron X-ray Studies of Al1-yTiy Formation and Re-hydriding Inhibition in Ti-Enhanced NaAlH4

NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotron X-ray diffraction in order to unveil the nature of Ti. No crystalline Ti-containing phases were observed after ball milling of NaAlH4 with the additives, neither as a solid solution in NaAlH4 nor as secondary phases. However, after cycling, a high-angle shoulder of Al is observed in the same position with 10% TiCl3 as that with 2% Ti(OBu)4, but with considerably higher intensity, indicating that the shoulder is caused by Ti. After prolonged reabsorption, there is only a small fraction of free Al phase left to react with Na3AlH6, whereas the shoulder caused by Al(1-y)Ti(y) is dominating. The Ti-containing phase causing the shoulder therefore contains less Ti than Al3Ti, and the aluminum in this phase is too strongly bound to react with Na3AlH6 to form NaAlH4. The composition of the Al(1-y)Ti(y) phase is estimated from quantitative phase analysis of powder X-ray diffraction data to be Al(0.85)Ti(0.15). Formation of this phase may explain the reduction of capacity beyond the theoretical reduction from the dead weight of the additive and the reaction between the additive and NaAlH4.

Crystal structure and stability of LiAlD 4 with TiF 3 additive

LiAlD 4 samples with TiF 3 additives have been investigated by synchrotron X-ray diffraction, neutron diffraction and a Sieverts-type apparatus. Directly after ball milling there are no signs of any Ti-containing phases, and the unit-cell of LiAlD 4 and Al give no indication of any solid solutions. Hence it is concluded that the Ti is in an amorphous state directly after ball milling. Furthermore, no LiF was observed in the samples. Based on Sieverts-type measurements the plateau pressure at 80 °C has been proved to be higher than 85 bar. Samples stored in a glove box are slowly desorbed, and after 6 months for a LiAlD 4 + TiF 3 sample, the reaction to LiD + Al is nearly finished.

Synchrotron X-ray and neutron diffraction studies of NaAlH 4 containing Ti additives

NaAlH 4, Na 3AlH 6 and NaH samples with Ti additives have been investigated by synchrotron X-ray diffraction and neutron diffraction. Directly after ball milling there are no signs of any Ti-containing phases, and the unit-cell dimensions of NaAlH 4, Na 3AlH 6 and Al give no indication of any solid solutions. Combined refinements of X-ray and neutron diffraction of Na 1−3 x Ti x AlD 4 and NaAl 1− x Ti x D 4 show no indications of such solid solutions. Hence it is concluded that the Ti is in an amorphous state directly after ball milling. After cycling, however, a shoulder on the high-angle side of the Al reflections appears that is interpreted as a fcc solid solution Al 1− x Ti x with x≈0.07. Furthermore, addition of TiF 3 by ball milling results in different phases compared to TiCl 3/TiCl 4. The chlorides give NaCl, whereas no NaF is formed by the fluoro additive. It has not yet been possible to determine by X-ray diffraction where the fluorine is in the sample.

An EXAFS and XRD study of the structure of nanocrystalline Ti - B - N thin films

Measurements of extended x-ray absorption fine structure (EXAFS) have been used in conjunction with glancing-angle x-ray diffraction (XRD) to study the structure of sputter-deposited nanocrystalline Ti - B - N thin films of various compositions. The chemical composition of the films was established by x-ray photoelectron spectroscopy and the equilibrium phase composition was calculated from an established phase diagram for the bulk Ti - B - N system. For the Ti - B - N layers low in nitrogen content a nanocrystalline -type structure in accordance with the predictions of the phase diagram was found. However, for a nitrogen-rich layer with the composition the expected Ti-containing phases, principally TiN, did not appear to be well formed. For this layer, the local structure around the central Ti atoms as deduced from EXAFS showed the Ti atoms mainly to be situated in disordered regions, possibly extremely small Ti - B or Ti - N clusters with no long-range crystalline order. The study has illustrated how the EXAFS technique can help one to understand the structure of poorly crystallized materials, especially in situations in which XRD measurements cannot be unambiguously interpreted.